1. Field of the Invention
The invention relates to a method for producing electrodes for electrolytic capacitors comprising a conducting electrode material. The material may be a foil such as an aluminum foil, which, for the purpose of increasing the surface area, is exposed to a chemical or electrochemical etching process. The invention also relates to electrodes produced with such a method.
2. Description of the Related Art
In the field of electrolytic capacitors it is known to use, for example, aluminum foils as electrode material, in which the aluminum foils have been subjected to an etching process in order to increase the effective surface thereof. In an electrochemical etching process, the aluminum foil is arranged, for example, between two conducting plates of an etching cell, and the plates are immersed in a conducting solution of electrolytes. The etching process can subsequently take place in different polarization configurations. For example, the aluminum foil can be connected to the positive pole of a current source and the conducting plates of the etching cell are connected to the negative pole of the current source, and a continuous or pulsed current flows. A further feasible configuration comprises disposing the aluminum foil between two conducting plates, between which an AC current flows. It is, in addition, known in the case of anodic foils to carry out an anodic oxidation after the etching process, which makes possible the growth of aluminum oxide on the foil surface. However, for specific electrolytic capacitors, electrodes with an etched surface are also frequently required in which, for example, in the margin region, connecting contacts must be applied. The electrode is to have good electric and thermal contact at these margin regions such that the equivalent series resistance (ESR) and the power consumption are improved when the electrodes are rolled up, for example, for the production of the electrolytic capacitor. Etching impairs such good contacts.
It is the object of the invention to provide in a simple manner electrodes which offer, in particular in their margin region, good electric and thermal contact.
This object is essentially solved by a method of the above described type in which, during the etching process, at least one zone of the surface of the electrode material is covered in the etching cell with an etch-resistant coating and/or by a separate protective shielding. After the etching process, the electrode is cut out, punched out, or otherwise worked out of the electrode material such that the non-etched zone forms at least a margin region, in particular a margin strip, of the electrode.
With this method, non-etched zones can be simply formed in any shape on the surface of the electrode material such that during the subsequent formation of the electrodes their margins are non-etched. Thus, the production method can be adapted to special requirements for specific electrodes. It is, in particular, possible to use sheet electrode material in the form of webs from which individual electrodes are subsequently punched out, such as in the form of strip electrodes which can be wound up. In this way, the production process can be standardized and made efficient for different electrode types, so that considerable cost reductions can be attained. In addition, the handling of large, for example web-form, foil material during the etching process is simpler than the handling of individual narrow electrodes. The provision of contact zones, which offer very good electric and thermal contact, can be omitted due to special surface working. The method according to the present invention is suitable for the production of electrodes used as anodes and cathodes.
In a simple implementation of the method according to the present invention for the production of these electrodes, a coating or foil can serve as a shielding deposition. The coating is applied onto the surface by, for example, application, emplacement, adhesion or the like, and after the etching, the coating is Such a method can be employed especially favorably, in particular, in the production of standardized electrode types.
It is also conceivable that a lacquer or a synthetic resin serves as the coating, wherein the lacquer or the synthetic resin is applied by spraying or by means of being brushed onto the surface. After the etching process, the lacquer or synthetic resin can be dissolved by an organic solution, for example. With such a method, a deposition, which has a complicated geometric shape, can also be readily applied onto the surface. In particular, when using a mask, the zones on the electrode material can be developed precisely.
In an electrochemical etching, the deposition is preferably developed as an insulating material, and during the etching process the deposition forms an electric shielding on the conducting electrode material. The insulating material can comprise, for example, an electrically nonconducting synthetic material, and is arranged between the electrode material and the conducting plates of an etching cell. In this case, the etching electrolyte is not in contact with the shielded zone since the insulating material is in direct contact with the surface of the electrode material such that no etching takes place in the shielded zones.
According to another implementation of the method, the protective shielding comprises a nonconducting material as a separate element arranged in the etching cell between the electrode material and the conducting plates of the etching cell such that the nonconducting material is in direct contact with the electrode material, and during the electrochemical etching process, the nonconducting material forms electric shielding.
The position of the protective shieldings in the etching cell can be handled especially simply, and allows for the desired non-etched surface of the electrode material to be readily reached during the continuous operation of the etching process. To this end, the protective shielding is already disposed in the desired geometry in the etching cell and does not need to be developed as a deposition in each instance on the electrode materials. However, a combination of both implementations of the method is also conceivable in which the protective shieldings, can, for example, also serve to fix the electrode material in the etching cell.
In the production of strip electrodes, the zones are preferably formed as parallel strips or the like, spaced apart from each other, defining regions extending in the longitudinal direction of the electrode material and developed, for example, as band material.
If the electrode is to be used as an anode, the electrode material is exposed to anodic oxidation after the etching. The deposition can be previously detached from the areas not to be etched, such that the etched and the non-etched zones are oxidized. For use of the electrode as a cathode, such treatment is not necessary.
The etching is preferably carried out with the formation of non-etched zones and, if appropriate, the oxidation is carried out on both sides of the electrode material. The non-etched zones can be developed on both sides of the electrode material corresponding to one another such that the electrodes formed therefrom have the same structure on both sides. In the case of special capacitor types, however, an asymmetric implementation of non-etched zones on the two sides of the material is also conceivable.
For the production of electrode strips from the, for example, web-like electrode material, corresponding electrode strips are cut out. Preferably, at least one longitudinal margin of the strip material is not etched.
Efficient processing of the electrode material is possible if for example, several strip-like electrodes are cut out of the sheet electrode materials.
The present invention further relates to electrodes comprised of a conducting electrode material such as a foil formed as a band material, for example an aluminum foil, with a surface which is etched on one or both sides and, if appropriate, anodically oxidized. In at least one margin region, preferably margin strips of the surface, at least one non-etched zone is developed. Zones can therein be disposed on each side of the electrode material corresponding to one another.
In the development of strip electrodes, corresponding strips are cut out of the, for example, web-form electrode material to have the width of the capacitor to be produced therefrom such that, preferably, at least one margin of the strip electrode is not etched.
Further characteristics, advantages and application feasibilities of the present invention will be evident based on the following description of exemplary embodiments and the accompanying drawing figures. All described and/or graphically shown characteristics by themselves or in any combination form therein the subject matter of the present invention, independently of their compilation in the claims or their reference back.